Plans vary from company to company but in general there are considerable advantages in having the company administer the program. Companies provide payroll deduction. This makes contributing easy and automatic. Companies frequently match a portion of the contribution the employee makes. This is a huge benefit.
Companies provide administration, record keeping and communication of the program.
Most absorb these costs. They also encourage employees to participate and will provide education and information to make it easy. 401k dollars can be invested in a wide variety of investments ranging from almost all kinds of mutual funds to individual stocks and bonds. Companies usually offer only a handful of investment selections. However, for the vast majority of 401k participants this is an advantage.