Free float and its impact

As I understand, free float is the % of shares available for trading. It seems logical that if the free float of a company is small, price changes could be more dramatic.

How much this should impact the buying decision for a specific stock?

Free float is the share that is freely available at ‘one point of time’ for selling and buying. The shares which are locked due to statutory requirements are excluded. Otherwise balance is technically tradable, Yes we take promoters shares as non free float, still they can sell with an intimation to stock exchange.
Saying that I take the big investors and promoters holding as not available for trading as their buying decision and selling decision are strategic in nature. When an institution sell without plan it can damage itself by pulling down the price.
If the free float is less and demand is high naturally stock will leap upwards as gap i.e. big strides. But can be double edge sword, at the time of selling it can drag the prices rapidly.
One has to use excellent capital protection plan for these shares, meaning once you are in profit make sure you sell into strength.
Otherwise as long term investor put a stop capital loss point and exit.