Between 2010 and 2015, the small cap index has given near zero returns. So be careful what you wish for, and what you invest in. See the BSE Small cap index below.
So staying invested for the long term does not necessarily mean a good thing.
Having said that many small cap funds have given great 5 year returns. Hence you can have this fund class in your portfolio, provided it suits your risk profile. Ideally a bunch of large cap funds, mid cap funds and multicap funds will do the job for most people.
Multicap funds have exposure to small cap stocks in any case. However if you wish to go for a small cap fund, do not go in with a mindset of rapid returns; stay invested and be smart; get out if there is turbulence.
Small caps have high mortality risk. Chor promoters abound and if you are not careful (even the smart fund managers), then the returns will not be great.
Take a free investment risk profile here to understand if small caps suit you.