It took me a while to find Phoebe Bright’s plugin so I’m commenting to help others that might be trying to find this.
I didn’t really like the explanations I’ve seen of what this add-on is or what it’s used for, and I had to read three different post to get a clear understanding. So here goes.
First of all the name seems a bit misleading. This thing is more about making SAEF easier and more flexible than it is about popups (just an opinion)
If you’re using custom_fields in your SAEF you probably want to show these fields with more flexibility than the standard {custom_fields}{/custom_fields} tag wrap.
This wonderful plugin lets you put your custom_fields in your SAEF without using the {custom_fields} tag wrap. The advantages are you can label, order, and style your fields with more flexibility than using the standard “tag wrap’ method. 
For dropdowns in an ENTRY form I use:
{exp:pops:pop_input field="job_type"}
<label for="{field_name}">Job Type</label>
{popup}
<input type="hidden" name="{field_format}" value="none" />
{/exp:pops:pop_input}
For dropdowns in an EDIT form I use:
{exp:pops:pop_input field="job_type" value="{job_type}"}
<label for="{field_name}">Job Type</label>
{popup}
{/exp:pops:pop_input}
If using in a SEARCH TEMPLATE, might want first value in the list to be Any
{exp:pops:pop_input value="{job_type}" field="job_type" first="Any"}
<label for="{field_name}">Job Type</label>
{popup}
<input type="hidden" name="{field_format}" value="none" />
{/exp:pops:pop_input}
For any other field types (textarea, text, etc.) I use:
{exp:pops:pop_input field="job_description"}
<label for="{field_name}">Job Description</label>
<textarea id="{field_name}" name="{field_name}" rows="6" cols="40">{value}</textarea>
<input type="hidden" name="{field_format}" value="none" />
{/exp:pops:pop_input}
This is a god send for me thanks to Phoebe Bright for such a great addition to the SAEF user community 
