We definitely won't be ABC valuebetting every time we hit. If we know villain is weak, or has a tendency to bluff when you show weakness, time to mix in slowplays. Against people who are observant, we want to strengthen our checking range, so that we can't be read so easily. Remember that it is very easy to play against someone who will indiscrimately value bet every time. Tight aggressive people tend to play like this.

Reasons why we will want to value bet our hands at micro and not bother too much with slowplays:
- Our value range is probably better balanced than the other people at the table, so because of this and bluffing, we can create an aggressive playstyle. This pressures people who face it, and force some to make big mistakes, like going broke on a big bluff or calling you down. Both on the frustration of "he can't have it every time". Same counts for an aggressive 3betting-style, but this is difficult to balance, so only tread there if you know what you're doing (ie, have good ranges for doing so).
- Some people will have difficulty laying hands down before the river, and will call an allin on turn a lot looser than they play on the river.
- Other people won't be phased by your aggressive playstyle (usually the multitabling regs). Recognize those people and exploit their tendencies. Here it can be ok to slowplay.