Leaving a wallet open 24/7 costs more electricity (and CPU power, more on this later) but also make you benefit more from compounded interest (interests adding to capital so that next time capital to base interest upon will be bigger - in a bank, you compound your interest once an year, in crypto, at the end of each period, so every twenty days for Mintcoin). If you received all of your coins in just one big transaction, you could just stick to open wallet at every stake period and this is it. You receive your coins, and they count for the next stake. But if you received them in several parts (99% of users) there are end-of-period occuring a lot and so opportunity for compounding interests occuring a lot (in other words, "it's every day twenty days"). By just opening you wallet every 20 days, you are actually losing compounded interest. Notice that with compounded interest, you should achieve more than 20% interest on Mintcoin (at the cost of electricity, though and less CPU-mining power, though). It is not worth it if you don't have a lot of coin (except if you don't pay for your electricity).
Beware though: the multiplication of the end-of-period generates "dust", something similar to fragmentation on a disk. This won't increase the size of your wallet, but it will require more CPU power. You may end up with 100% CPU usage. Raspberry or VPS are ways to mitigate this. Another way is to resort to "spring cleaning": every once in a while, you move all your coin to another wallet; you sacrifice every coin age to get back to a normal level of CPU usage. Heartbreaking.
I just found the reason why my laptop battery un-charges so quickly. Thanks for the heads up!
