Is it safe to enable to allow apps from unknown sources?

I would like to install whatsapp on my Huawei android tablet but get the message (as others have ) stating ' your device is not compatible'. Searching the internet it seems that you can bypass things and get it installed. However it seems the only way to do it is to all apps from unknown sources. My problem is I am not happy in what you appear to be doing ie withdrawing security and allowing apps from unknown sources. Does anyone know if it really is safeand will not allow the tablet to add peculiar and potentially other unwanted app thanks