There is a fine line of difference between IIS Reset and Web Application Pool recycle when it comes to SharePoint Deployments.
IIS Reset does 2 important things concerning SharePoint -
- It recycles all your application pools at one go and clears the memory objects.
- It reloads all dlls from the GAC(global assembly cache) in the farm servers.
Web Application pool recycle is concerned with both the above for all IIS websites sharing a single APP Pool.
Considering the above, when you deploy a farm solution whose scope of activation is at the web application level, SharePoint only recycles the application pool of that target web application where the farm solution is to be deployed. In most cases from the perspective of IIS it is just one website.
This is not an IIS Reset. Your all other web applications in SharePoint will continue to work just fine retaining their existing http requests queues and asp.net objects in the app domain.
Coming to your question regarding timer job and page layout changes.
Think of SharePoint deployments in two different categories :-
a) Functional Changes
b) Branding Changes
Predominantly all of SharePoint deployments more or less fall into these two categories.
Functional Changes - These include your farm solutions like timer jobs, webparts, event receivers, custom dlls (like MVC data access layers),etc.
These changes are dll driven and hit the GAC of each server added in the farm. So there is a dependency on web application pool recycle and IIS resets in such deployments.
Branding Changes - Masterpage , CSS , site templates , images ,etc. While most of these changes can be and "should be" deployed through a visual studio solution for the sake of release tracking and version control, you can make certain exceptions when it comes to deployment images. css files for a internet facing website.
Under such scenarios, you can certainly replace the existing files in the 14 hive folder physically for all your web front end servers if your internet facing site calls for zero downtime.
In this case, you wont need an IIS Reset and users get to see the branding changes with a page/cache refresh in their browsers.