Paul
It's neither a good idea nor a bad idea.
About ten years ago in the days of the original Google Page Rank, these sort of links were incredibly powerful and made a big difference.
In those days we had mass submission software like SEONuke GSA and
Magic Submitter that could build several thousand a day. We also built profile links (where you put your link in your membership profile on each site). It used to cost a lot in Capcha solving fees but at that time, Google gave them a lot of clout.
Eventually, as Mark said they got devalued and nowadays building a few by hand is pretty much a waste of time for ranking. You might however get some traffic via the links, so maybe a few on the right sites may work.
They still have their place alongside a host of other things but normally have to be done in huge quantities. I've just had a quick look on Fiverr and you can get 600 hand posted for £339.95, 200,000 auto-posted for £71.77 and ten million GSA links done for £ 37.77 ! Then you have to actually get them indexed, which may never happen. They are useful if used in the right way but plain stupid if you don't know what you are doing.