The following post might sound somewhat paranoid but it isn't. I (try to) just report facts which another commenter said "everybody knows already anyway".

So:
All email are parsed for shopping info (price, product, quantity), shipping/tracking numbers (UPS, FedEx etc.), upcoming bills or reminders, what they are for and in which amount, dates & events (flight numbers, passenger names, booking codes, events, invitations, collaborations).
How you deal with each email (delete it unread, categorize it or send it to spam) is also recorded and over time influences the behavior of your inbox (depending on your settings as well). Who sends you email and which groups of users you send email to (this will be used to identify your peer groups and Google will recommend you add a person if it thinks you forgot to CC them in an email).

All your attachments and all their contents are processed (to search for malware and/or illegal content).

All files you store on Google Drive are continuously monitored for size and content which might be illegal (such as porn) etc. and how many people look at them (if you share it with too many people, your account may be closed).

All your photos uploaded to Google Photos are used to train machine-learning algorithms for facial recognition and item identification.

All files on Google Drive that you delete, are not deleted right away.

All the Wi-fi passwords of networks you connect to on the phone, all Wi-Fi networks you pass but don't connect to and all the Bluetooth devices you connect to will also be stored (Google uses these for better location information if or when GPS is unavailable).

By default, if you are logged into your Google account while surfing the web and/or using Chrome, Google will also collect, store and connect with your identity

- each and every phrase you search (this feature is called Web Activity)

- all the apps you use, how often and how long (App Activity)

- every video you watch on YouTube, how long and whether you skip certain parts (this feature is called YouTube Search & Watch History)

- every location you visit with GPS enabled on your phone and/or navigate to using Google Maps (this feature is called Location History)

- all voice commands you input into Google search or Google assistant (this feature is called Voice & Audio Activity)

- any voicemail you receive on Gmail (through Google Voice) will be transcribed

This will be used to show you personalized ads but it will also be aggregated and used to analyze trends and patterns.

This is all on top of the usual stuff that Google collects by tracking you regardless of whether or not you are logged into your account, by virtue of having the largest ad network in the world which is embedded on all major websites.

You can find much of that information on myaccount.google.com and more if you order a "Google Takeout" which will allow you to download all the info that Google has about you.

If you use Google Enterprise accounts, your admin can additionally configure it so they can:

- see and read all emails you send and receive, and whether you opened them

- see any and all email you have deleted (they will be hidden from you but not deleted)

- see all chats (Hangouts), their contents, times and who participated.

This feature is called Google Vault, Litigation Hold and eDisovery and costs extra (but is included in some of the higher tiers).
Note that using this feature to access emails other than your own is illegal in some EU countries but not in the US.

What Google does NOT track:

- Recordings from your cell phone's microphone or camera. People occasionally claim that they get ads for a certain product just because they talked about it with their phone in the room. But that's coincidence or due to the fact that advertisers know which people are in vicinity of each other (family, location, same IP) and one of their peers searched for it, so the ad is shown to all people in that network etc. (more complicated than that but that's the gist).

Whether or not the tracking appears malicious to you probably depends on whether you think Google is evil or not. Better hope that they aren't ;-)

Disclaimer: Some of the info I mentioned might not be up-to-date. You can switch off some but not all of those "features". You can set auto-delete time frames for some but not all of these, too. Whether they are actually deleted or just hidden, who knows.
If I made an error or you disagree, please don't mindlessly downvote but reply and correct me. Thank you.