yes, in a simplistic way, the piston extend while the spring "shrink", so you can achieve a kind of "in" and "out" using a combo of piston and spring. But the behavior of each one is totally different.
Ex:

The piston moves accurately one block ahead in parallel motion. You CAN'T do that with a spring. That's why i think a "reverted" piston is wellcome.
The same goes to the spring, sometimes you don't want accurate/parallel movement. You want to hold something tightly (as a hope, or a chain) and then with a button press, you release its tension and let it flex.