Once your lock period ends you are free to withdraw your staked Coins but you do not have to withdraw your funds. They can stay in the pool and keep generating/compounding rewards at the same rate as when they were locked.
When you compound on a locked amount it joins and does not start a new lock time.
Ex: If you have 1000 coins in a 90 day lock pool (40%) and you compound on day 10 then your new total will still unlock in 80 days. It does not restart the timer.
However, a new deposit on top will begin a new timer for that amount.
Ex: 1000 GroveCoin in the 90 day lock pool. On day 10 you add a new stake of a further 100 coins.
The 1000 coins will unlock 90 days from stake time (Day 90 of using the pool)
The 100 coins will unlock 90 days from stake time (Day 100 of you using the pool)
Earnings are calculated on the total staked amount (1100 coins in the example) but join the longest remaining lock period (Day 100 unlock).