Really the biggest gains are from holding it. Just immediate mining can be ok but as difficulty changes and price with supply and demand that is when your mining last month appears very profitable.
I am personally a miner, and I keep all I mine. I just sell from times to times what I need to pay for the electricity but that's all. Time said me I was right and with my predictions in the crypto-currency market, I will be right another time.
Not sure about holding for very long amounts of time though because electricity bill can be large and the price can always fall back down. I wouldnt carry from year to year without selling because of that, month to month is ok till time for paying off costs. Recently bitcoin and many coins in general have been appreciating.
This makes 2016 look like an excellent time to have been saving or holding coins. Its doubtful holding mining from now till next year will look just as good as that. Its not impossible but I imagine at least growth slows down.
I always swap some crypto over to gold, its price trends over decades and has been a way to hold value a long time. I think of that money as asset money more then spending money, for times you need security and deposits more then paying bills. Always hold some I agree but never hold all one thing