As the title says really.
Do you do a brief for your clients, gannt charts, wireframes and prototypes?
I assume these can be very time consuming tasks, but is it worth the benefit?
My concern is that they may take up a lot of time especially on smaller projects and increase development costs.
Very little of my work is for clients directly but it’s an area we are planning on moving into and something we are Keen to learn more.
Yes, and I also do sitemaps, audits, consultancy, mock-up’s and other forms of Information Architecture when it’s required. 
It depends, a wireframe could be anything from an architects blueprint (in terms of detail) right down to a doodle on a napkin, as long as you get the point across and have it clarified with the client it’s well worth the pay-off as you may as well try and get it right the first time around (if only for your own sanity).
I would say development costs would be reduced, you’ll have less tweaking and redesigning to-do (as stated earlier). Why waste time re-doing the work when you can spend a bit of extra time at the start to ensure it’s right. If a small project is straight forward, you may not need to go into so much depth but like with all things, these kind of solutions are tools to aid you simplify a complex process. If you feel that the project could benefit from them, use it!
yes, we do them. we may not do all of them for each job, it really depends on the scope. the bigger the project, the more upfront planning we do. just like tke71709 said above, i hate to redo work.
You must brief the clients with a view to build confidence about you in them. If the project is a large scale one then you should also make use of prototypes.
Spend the time at the beginning of the project or spend more at the end.
Do you do a brief for your clients, gannt charts, wireframes and prototypes?
Yes. There are reams of articles and a trail of failed projects to explain why.
My concern is that they may take up a lot of time especially on smaller projects and increase development costs.
You really have to go into the ditch a few times to stop asking this. Nothing anybody tells you will make a lick of sense until then. You’ll nod politely, then go about running into the very next ditch.
You can nod politely to the following…
Taking the “You” Out of User: My Experience Using Personas
Yeah, yeah. Yes - but. Yes - but. Yes - but. And a half dozen excuses about why your project is really truly not covered by this. Don’t bother.
Real Wireframes Get Real Results
There is exactly one, legitimate, exception. A site or app built without a purpose, just to have a site. And excuses are not purposes.
Never Get Involved in a Land War in Asia (or Build a Website for No Reason)
Building a site for “the user,” “the market” but you couldn’t pin down a specific human trait to save your life? That’s a site without a purpose. You’re making a site for your imaginary friend, “the user.”
You discard these tools when the client wants a site in the worst way possible. And you decide to give them exactly that.