If you have a small penis, you might actually be able to do something during front-entry (missionary) PIV that a finger can do but a medium-to-large penis can't: stimulate the G-spot to the fullest possible extent. This is because if you tried this technique bigger dicks, you'd be too rough.

All you have to do is get your dick partly in (or all the way in if you're particularly small) while angling your dick upwards during the initial entry. This means having your hips lower than they usually would be, or your partner's hips held up higher. This allows your tip to poke directly into the g-spot with enough force to stimulate it with sexual pleasure, but not enough to cause an abrasion. This way, if you hit it like that for long enough, you can make your partner ejaculate or squirt through PIV alone, which people with larger penises can only dream of doing most of the time!