Marionette and mindymouse1 have pretty well summed it up.
I started mine with $10.00 back in 2015 to get the clock ticking. I waited about a year before I put anymore $$ in the account. I have used it with some trepidation due to some of the problems folks have reported. I use it much in the way Marionette describes above--I put the money in just before a major purchase and then I use it right away. I prefer to use a CC, but sometimes I receive gift cards at Christmas and it is a convenient way to aggregate them.