Google Ads and Google Local Service Ads are two separate Advertising products by Google that operate differently with different requirements, and Ad placements.
Google Ads
Charges on a cost-per click basis. No refunds.
Primary actions for leads: Ad click to website (destination URL) ; Calling via Ad Extension ; Map Pack Ad click.
Tends to be more expensive per lead.
Provides more flexibility to target specific keywords/Searches that Google Local Service Ads does not target unlike GLSA (e.g. 'metal roofing' not targeted by GLSA; 'metal roofer' targeted by GLSA).
More control over the destination (URL) that someone reaches after clicking your Ad.
More performance factors involved, requires more expertise for setup and optimization (not talking about Smart campaigns).
Google Local Service Ads
Easy setup and relatively quick results.
Primary actions for leads: Calling ; Messaging ; Booking ; View Local Service Listing.
Charges on a cost-per-lead basis & bad leads are refundable. Dispute needs to be filed.
Provides little to no flexibility for more granular targeting.
Fewer performance factors involved, requires google guaranteed, quick lead response rates, consistently new reviews, consistent lead updates, and optimal budget to rank high.
Does not require a website to get started.
Requires a background check. Requires a Google Business Profile and other requirements may apply based on your service type, to get started.
To Conclude
Google Ads and Google Local Service Ads work best together to cover the top of Google with multiple of your Ad placements. This is also the recommended approach by Google.