You will probably find a magnet holder much more convenient than laying the brush across the top of the can. A brush laid across the can often gets paint on the handle and then onto your hands. Place a small amount of paint in the middle of a paper plate. Place the paint can in the paint. The plate will stick to the can and catch any drippings from the brush.
Paint always seems to build up in the lid groove on the can during every painting job.
This often causes paint to run down the side of the can. These holes permit the paint to drain back into the can each time it accumulates in the lid groove. These holes in no way affect the resealing of the can, since the lid seals by pressure on the sides of the groove rather than on the bottom. Put any leftover paint in a quart can and seal it tightly-use the regular lid for the can if it is available. The plastic lid makes an airtight seal to keep the paint in good condition until you use it later.