Depending on where most of your visitors are coming from. Activating HTTPS may lead to slower page loading times if your visitor’s computer system or Internet access is not modern or server is not equipped to deal with all the SSL requests. Otherwise, there is no reason you shouldn’t direct your visitors to the secure version of your site.
Users that are using old computers and non-modern web browsers may receive popups about your site when they try to visit if your SSL certificate is issued by a Certificate Authority not recognized by their browser. Your users may also face slower load times if your site is media heavy (a lot of images or videos) and this is all be serving over a HTTPS connection. Depending on how your server is set up it may lead to a spike in memory and CPU usage.
When all your visitors are accessing your site via a HTTPS connection. There will be an increase in CPU resource and memory usage. If your server has plenty of resources readily available then you should be good to go. If not and you receive a surge in visitors over a HTTPS connection your server may have issues processing everything.
Google and other search engines will probably begin favoring sites that serve up content over a secure connection compared to non-secure connections. Having a secure connection of your site available will help your website gain your visitors trust more. It will also help make your server’s connection to your visitors computers secure from eavesdropping.