You use the terms, seemed and got the impression, you have to be more specific about what it uses on your system before and after as there is nothing to compare against.
Yes avast uses some more resources in this 4.8 version than it did in the 4.7 version, but it is still light in comparison to many other AVs and in the greater scheme of things resources (I assume you mean RAM) as a percentage of your system RAM is minuscule.
Though you don't give us any information on your system and the possible impact on your resources, CPU, RAM, other applications and Security applications running, etc. Hell I look at Task Manager not the best to gage actual memory use and firefox uses more memory than all of avast combined so does Windows Explorer, so does my Firewall.
So we need to get things in perspective, resources are there to be used and if necessary managed. But given the improvements in avast 4.8 and a slight increase in resources I see no appreciable difference in my system responsiveness and I have no speed machine.