To control the memory of WhatsApp on your phone you may notice that
WhatsApp has an option where you can view your contacts and how much space each is taking. Go to WhatsApp> Storage and data usage>Storage usage.
Now you will see all your recent chats along with the space each is consuming on your phone. Select the chat>Manage messages>Clear messages.
WhatsApp make your phone slow in following scenarios :
- Say, your running on low memory and if you have the setting of backing up chat data of WhatsApp on daily basis. In this case, the whatsapp backup data can create a problem for your phone as it will take space when your are running out of it.
- Another scenario is when you have many chats in you WhatsApp history and you don’t tend to delete it. If you have many chats opened, then their datas like images, videos (in case you have opted for storing videos too in the backup) etc can take huge space in the chat backup and will result you in slow processing if you have low RAM and Rom in your phone.
- When you have low RAM and ROM and you keep your WhatsApp running in the background then, it might affect the performance of your phone but not otherwise.
Which means in general , on average scenario a WhatsApp running on an average smartphones (not too much basic smartphone), does not create any lag or slow processing.