Remember the goal is to win moniez not hands... so play big hands for big pots, small hands for small pots. Big TPTK or overpairs are big hands pre-flop... they become smaller as you move through the streets. Drawing hands start smaller and need good implied odds to let you see as many streets as possible... which is much easier with a smaller starting pot... and then when they hit (and become big...) your problem becomes building the pot to maximize value (a high class problem to have ) And finally, one pair (and even two pair) hands don't play well with others... they're bigger heads up and get smaller the more people are in the pot. Straight & flush draw hands (and to lesser extent sets) do great multi-way so we're keeping people in.

Raise to build big pots (for big hands) and limit the field (for hands that play better HU)
Limp to benefit from a maller pot (for small or drawing hands) and to keep people along for the ride (optimizing your implied odds)

Also, keep in mind that "big" and "small" are all relative to the size the stacks involved in the hand. A 10BB pot is "big" when it's just you and a 20BB short stacker. The same pot is "small" when you're 90BB deep.

Load in a sh!tload of "it depends" and other stuff and I hope there's something in there that helps. If not... mech, I won't be offended...