Subscribing to any online data source (such as Ancestry or FindmyPast) will give you access from the comfort of your own home to records that might not be easily available to you (or available to you at all) by any other method. All the online providers are working hard to increase their attractiveness by offering an increased range of records for you to search and additional facilities such as online family trees, 'hints' to help your research along, and facilities to link up with other researchers interested in the same ancestors. Whether the additional facilities are worthwhile for you really depends on the way in which you work and the stage you're at in your research.
If you are considering subscribing to any paid site, check first that the site has sufficient records of interest to you, and whether there's a more cost-effective way of accessing the same data. FamilySearch are working hard to increase the data they make available and what isn't online can often be made available at a (relatively) local FamilySearch center. And many libraries (at least here in the UK and possibly elsewhere) can provide you with access to subscription sites from PCS on their premises.
If you do decide you want to try out a site such an Ancestry, sign up for a free trial first -- and plan to do it when you have plenty of time available to reap the benefits and assess whether you want to continue paying. And don't forget to terminate the trial if you decide not to go ahead!
Don't forget as well that there will always be records you cannot access online, perhaps because their custodians are unwilling to allow it or because they are of such limited interest that nobody will fund making them available.
And finally, take the advertised record coverage with a pinch of salt. For example, Findmypast boasts a unique complete collection of online Welsh parish registers. Which is complete apart from the parishes where the incumbent declined to share the data. And a number of sources will offer you records of passengers travelling to or form England -- without being completely clear about the limitations of the record set they've been given access to. If a particular record set is vitally important to you, try to understand when Ancestry (or whoever) got their data, so you can assess how complete it is going to be.